In a white house on a quiet, leafy street in Takoma Park, Md., lives a man who listens to nothing but mayhem. He is remarkable not because of his appearance — tall, thin, black hair — but for what he has around him at all times: scanners.

On this day, the scanners of Alan Henney — whose tweets of bedlam are followed by dozens of Washington journalists — were going full blast. Eleven cluttered his coffee table and living room, all tuned to different radio frequencies from across the region. There was the chirp of D.C. Fire and EMS responders. The prattle of dispatch in Prince George’s County. And the broadcast of Montgomery County officials telling of a traffic accident, which, Henney concluded solemnly, “doesn’t sound very good.”

Something else that didn’t sound very good: the garbled noise coming from one scanner, obscuring D.C. police chatter. To Henney it sounded like death — not the death caused by crime or traffic accidents, but the demise of a passion.

Across the United States, there are hundreds, if not thousands, of people like Henney who listen to official communications on radio signals, sifting through a morass of chatter for interesting news. Some pester crime reporters with tips. Others, such as Henney, showcase the hard-won news items — like gem hunters would a stone — on their social media feeds. But soon, Henney fears, all of that may end. And what will become of the scanner enthusiasts when there’s nothing left to scan?

Over the past few years, an increasing number of municipalities and police departments, including the District’s, have begun encrypting their radioed communications, a trend driven in part by fear that bad guys and terrorists need to do little more nowadays than download a police-scanning app to get all the intelligence they need on what police are doing and where. Just this year, police in Las Vegas, Richmond and Knoxville, Tenn., have encrypted their radio communication.

But what police are calling a public safety measure, scanner hobbyists are describing as a blow to transparency. Now they’re asking plaintive questions about whether it portends the end of a pastime once incubated in science clubs and Scout groups.

“Who’s to blame? Who caused it? . . . What’s the future?” despaired one enthusiast in a YouTube video shot amid his scanners and wires.

In the D.C. region, the keeper of the scanners’ code, and a source of stability in these turbulent scanning times, is Henney — director of the Capitol Hill Monitors group, publisher of the Capitol Hill Monitor periodical and author of the 534-page Washington-Baltimore Scanner Almanac. He spends his days at home now, tending to his ailing 87-year-old mother, planning annual regional scanner gatherings, listening to the channels he still gets and tweeting updates in the staccato voice of a just-the-facts-ma’am newsman. Meanwhile, he apportions blame for the possible collapse of his obsession.

High up on the list: Radio Shack.

There was a time when Henney was getting started — just a boy and his scanner, given to him by his father as a birthday gift — that Radio Shack was a haven for enthusiasts like him. But then the company pivoted from the radio to other electronics — and the sense of disillusionment in the scanning community was great indeed.

“Abandoned,” Henney mourned. “Many of us felt abandoned by Radio Shack.”

It was only the beginning. Police and other public safety agencies started switching to a more complicated trunked radio system, requiring the purchase of additional equipment and sending the expense of the hobby soaring. Then came the terrorist attacks of 9/11 and, with it, increased concern over securing communications. More recently has arrived a new generation of Americans who are less enamored of the radio waves, preferring social media and newer technologies.

“I’m not saying enthusiasts my age do not exist,” said Kenny Lorber, 27, who also volunteers with the Montgomery County Park Police. “But they are definitely dwindling.”

So, too, are the number of people going to Henney’s annual scanning meetings, plunging from a height of about 50 people in the 1990s to fewer than half that number these days. Even longtime scanning buffs have started dropping out.

“In November, I turned 80 years old,” said Willard Hardman, who wrote the scanning almanac with Henney. To him, scanning is no longer “cost-effective.”

“As a result,” he said, “I sold or gave away my equipment and left the hobby.”

Those who have left, and those who aren’t willing to take up the avocation in the first place, are missing out on what scanning buffs describe as an unfiltered, fully texturized reality — undiluted by information gatekeepers such as journalists and spokesmen.

“This radio traffic really gives you the pulse of the city and makes you realize how many stories are not being told,” said Luke Berndt, who got into this when he was living near the Adams Morgan fire station and his daughter kept wondering where the trucks were going. The answer, it often seemed, was to tend to an overdose. This was an event, he learned, that occurred thousands of times every year in the District but was rarely reported.

This plumbing of a city’s underside, accessing knowledge few have — all of it mingles to yield an intoxicating feeling that has kept Henney, who supports himself with rental properties in Delaware’s Rehoboth Beach, coming back for more.

He now stood for lunch. He buckled one scanner onto his belt. Then he put on a black vest with big cargo pockets. Into each, he fitted a scanner. He started for the door wearing five or six scanners and got into a car fitted with two extra radio antennas and equipped with a catalogue of radio channels.

“What if something big happens and I miss it? I don’t like to miss stuff,” he said by way of explanation as he drove to Mark’s Kitchen, a Takoma Park restaurant. There, he set up shop at a side table, arraying his scanners before him. Sometimes people look at him a little funny, but he rarely pays attention. His focus is on the news that could happen at any moment.

So far that day, there had been only one bit of news that he said “rises to the level of a tweet.”

It hadn’t been big. Just an all-terrain vehicle crash near Camp Springs,Md., with “serious but hopefully [nonlethal] injuries for the ATV rider,” as he’d reported. But it had been big enough: Enough for the public to know. Enough to distract him from the feeling that one day he may not have any more news to share.

Back at his house an hour later, he saw no one had followed up on his tip. But maybe someone would with the next one.